The present disclosure relates to a stirring/conveying member that conveys, while stirring, powder such as developer, to a developing device provided with such a stirring/conveying member, and to an image forming apparatus incorporating such a developing device.
In image forming apparatuses, a latent image formed on an image carrying member comprising a photosensitive member or the like is made visible by being developed into a toner image by a developing device. Some such developing devices adopt a two-component developing system that uses two-component developer. In this type of developing device, developer containing carrier and toner is stored in a developer container, there is arranged a developing roller which feeds the developer to the image carrying member, and there is arranged a stirring/conveying member which conveys, while stirring, the developer inside the developer container to feed it to the developing roller.
In the two-component developing system, insufficient electrostatic charging of toner may lead to image defects such as splashed toner and a foggy image. Thus, it is necessary to sufficiently stir and mix toner and carrier together to electrostatically charge the toner to a predetermined charging amount.
As a solution, a powder stirring/conveying member is known which includes a shaft member, a main conveying blade which conveys powder in a first direction toward one side of the axial direction as the shaft member rotates, and a sub-conveying means which exerts on part of the powder a conveying action in a second direction toward the other side of the axial direction as the shaft member rotates. As the sub-conveying means, a sub-conveying blade is known which has a smaller diameter than the main conveying blade and which spirals in the opposite direction (opposite phase) to the main conveying blade.
A stirring/conveying member is known which includes a rotary shaft, a first helical blade which is formed on the circumferential surface of the rotary shaft and which conveys powder in the axial direction by the rotation of the rotary shaft, and a second helical blade which is formed on the circumferential surface of the rotary shaft to overlap the forming region of the first helical blade, spirals in the opposite phase to the first helical blade, and has a smaller radial diameter than the first helical blade. In this stirring/conveying member, the first helical blade and the second helical blade have a trapezoidal sectional shape on a plane traversing the helical blades in their longitudinal direction. In the first helical blade and the second helical blade, there are respectively formed a plurality of first expansion portions and second expansion portions where the base part of the trapezoid expands wider than elsewhere in one turn about the rotary shaft. The first and second helical blades cross each other at least at one place at the first expansion portion in one turn about the rotary shaft.
With the above configurations, the second helical blade (sub-conveying blade) exerts a conveying force in the direction opposite to the developer conveyance direction of the first helical blade (main conveying blade), and thus convection occurs on part of the conveyed developer; this promotes the stirring effect with almost no interference with the conveying action of the first helical blade (main conveying blade). As a result, the stirring/conveying member can, while retaining both the conveying force of powder such as developer and the stirring effect, avoid applying excessive stress to the powder and is excellent in moldability.